The proposed research will concentrate on the interaction of avian RNA tumor viruses with cells of hematopoietic origin. The transforming events of AMV and RSV will be studied in a quantitative fashion. Conditional viral mutants of AMV will be studied with the aim of defining viral gene functions which are responsible for neoplastic transformation. The possibility that endogenous viruses with transforming ability, could be recovered from chemically-transformed avian cells will be examined. The hypothesis that lysosomal breakage may play a role in virus-induced plaques will also be examined.